The disclosure of Japanese Patent Application No. 2000-213910 filed on Jul. 14, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a technology for cooling a fuel cell in a fuel cell system.
2. Description of the Related Art
Fuel cells that generate electric power by utilizing an electrochemical reaction between hydrogen and oxygen are expected as a next-generation energy source. During operation (power generation) of a fuel cell, a considerable amount of heat is produced by the electrochemical reaction. Therefore, an ordinary fuel cell system has a cooling apparatus for cooling the fuel cell.
Japanese Patent Application Laid-Open No. 8-184877, for example, describes a cooling apparatus of a fuel cell system. In this apparatus, the fuel cell is cooled through the use of a coolant that includes an antifreezing solution containing water and ethylene glycol.
However, since the antifreezing solution containing water and ethylene glycol is capable of conducting electricity, it is difficult for the aforementioned prior art cooling apparatus in some cases to maintain a sufficiently high level of insulation of the fuel cell system.
It is an object of the invention to provide a technology that allows an easy improvement in the insulation of a fuel cell of a fuel cell system.
A fuel cell system is provided with a fuel cell and a cooling apparatus that cools the fuel cell. The cooling apparatus of the fuel cell system includes a first forced circulation cooling system that cools the fuel cell by forcibly circulating a coolant through a circulation passage that extends through the fuel cell. The cooling apparatus uses an electrically insulating solution as a coolant contained in at least a portion of the cooling apparatus.
In this fuel cell system, the fuel cell cooling apparatus uses an electrically insulating coolant, so that the fuel cell can easily be electrically insulated from the outside. Therefore, it is possible to enhance the insulation of the fuel cell system easily.
The cooling apparatus of the fuel cell system is provided with a second forced circulation cooling system that is independent of the first forced circulation cooling system, and an intermediate cooling system that is operable to exchange heat with the first forced circulation cooling system and with the second forced circulation cooling system. The intermediate cooling system contains the electrically insulating solution as a coolant.
Since the coolant used in the intermediate cooling system is an electrically insulating liquid, this construction eliminates the need to consider electrical insulation with regard to the first and second forced circulation cooling systems. Therefore, it is possible to enhance the insulation of the fuel cell system easily.
The intermediate cooling system of the fuel cell system has a container that houses therein the electrically insulating liquid. The electrically insulating solution exchanges heat with the first forced circulation cooling system and with the second forced circulation cooling system while naturally circulating in the container.
This construction has an advantage of simplifying the construction of the intermediate cooling system.
The electrically insulating liquid contained in the intermediate cooling system of the fuel cell system is allowed to boil in the container with a heat derived from the first forced circulation cooling system.
If boiling heat transfer is utilized, the rate of heat transfer to the electrically insulating liquid increases. Therefore the cooling efficiency can be improved.
Each of the first forced circulation cooling system and the second forced circulation cooling system has a heat exchange acceleration portion that accelerates heat exchange with the electrically insulating liquid in the intermediate cooling system.
This construction may improve the cooling efficiency of the intermediate cooling system.
The second forced circulation cooling system has a heat dissipation portion that dissipates heat to an atmosphere.
This construction may improve the cooling efficiency of the second forced circulation cooling system.
The electrically insulating liquid has an antifreezing property.
This construction may expand the temperature range in which the fuel cell system can be operated.
The electrically insulating solution includes a fluorine-based inert liquid or an insulating oil.
A fluorine-based inert liquid or an insulating oil is electrically insulating and antifreezing properties, and therefore are preferable as an electrically insulating coolant.
The invention may be realized in various forms. For example, the invention can be realized in the form of a fuel cell system, a fuel cell cooling system, a cooling method, and the like.